In a study reported in the Journal of the National Cancer Institute, Ahn and colleagues found that decreased diversity of gut bacteria and differences in levels of specific bacteria were associated with significantly increased risk of colorectal cancer.

Clostridia ferments dietary fiber and other complex carbohydrates to butyrate, a major colonic metabolite that may inhibit colonic inflammation and carcinogenesis. Fusobacterium contributes to colitis and periodontal disease. Atopobium is associated with Crohn’s disease and has been reported to inhibit colon cancer apoptosis in vitro. Porphyromonas is commonly found in the mouth and gastrointestinal tract and is associated with periodontal disease.

The investigators concluded, “Because of the potentially modifiable nature of the gut bacteria, our findings may have implications for [colorectal cancer] prevention.” ■